CO2 recovery system and method

ABSTRACT

A CO 2  recovery system includes an absorption tower and a regeneration tower. CO 2  rich solution is produced in the absorption tower by absorbing CO 2  from CO 2 -containing gas. The CO 2  rich solution is conveyed to the regeneration tower where lean solution is produced from the rich solution by removing CO 2 . A regeneration heater heats lean solution that accumulates near a bottom portion of the regeneration tower with saturated steam thereby producing steam condensate from the saturated steam. A steam-condensate heat exchanger heats the rich solution conveyed from the absorption tower to the regeneration tower with the steam condensate.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a Divisional of U.S. application Ser. No.10/592,746, filed Jul. 9, 2007 and now U.S. Pat. No. 7,918,926, andwherein application Ser. No. 10/592,746 is a national stage applicationfiled under 35 USC §371 of International Application No.PCT/JP2005/004473, filed on Mar. 14, 2005, which claims priority ofJapan Application No. 2004-073388, filed Mar. 15, 2004, the entirecontents of which are herein incorpoated by reference.

TECHNICAL FIELD

The present invention relates to a CO₂ recovery system and method forachieving energy saving.

BACKGROUND ART

In recent years the greenhouse effect due to CO₂ has been pointed out asone of causes of the global warming, and a countermeasure against it isurgently required internationally to protect global environment. CO₂sources range various fields of human activities, including burning offossil fuels, and demands to suppress their CO₂ emission from thesesources are on constant increase. In association with this, people haveenergetically studied means and methods for suppressing emission of CO₂from power generation facilities such as power plants which use anenormous amount of fossil fuels. One of the methods includes bringingcombustion exhaust gas of boilers into contact with an amine-basedCO₂-absorbing solution. This method allows removal and recovery of CO₂from the combustion exhaust gas. Another method includes storingrecovered CO₂, i.e., not returning the recovered CO₂ to the atmosphere.

Various methods are known to remove and recover CO₂ from combustionexhaust gas using the CO₂-absorbing solution. One of the methodsincludes contacting the combustion exhaust gas with the CO₂-absorbingsolution in an absorption tower, heating an absorbing solution havingabsorbed CO₂ in a regeneration tower, and releasing CO₂, regeneratingthe absorbing solution, and circulating the regenerated absorbingsolution to the absorption tower again to be reused (Patent document 1).

Patent document 1: Japanese Patent Application Laid-Open No. H7-51537.

DISCLOSURE OF INVENTION Problem to be Solved by the Invention

In the conventional method, however, the steps of removing, andrecovering CO₂ from CO₂-containing gas are provided additionally incombustion facilities, and hence, the operation costs should be reducedas much as possible. Particularly, among the processes, a regeneratingprocess consumes a large amount of heat energy, and therefore, theregenerating process needs to be provided as an energy saving process asmuch as possible.

The present invention has been achieved to solve the problems, and it isan object of the present invention to provide a CO₂ recovery system andmethod in which an energy efficiency is further improved.

Means For Solving Problem

To solve the above problems, a first aspect of the present inventionrelates to a CO₂ recovery system including an absorption tower thatcontacts CO₂-containing gas with a CO₂-absorbing solution to remove CO₂and a regeneration tower that regenerates a rich solution havingabsorbed CO₂, and reusing a lean solution, obtained by removing CO₂ fromthe rich solution in the regeneration tower, in the absorption tower,comprising a regeneration heater that extracts the lean solutionrecovered near a bottom portion of the regeneration tower to theoutside, and heat-exchanges the lean solution with saturated steam; anda steam-condensate heat exchanger that heats the rich solution to besupplied to the regeneration tower or heats a semi-lean solutionobtained by removing part of CO₂ from the rich solution, with residualheat of steam condensate fed from the regeneration heater, the semi-leansolution having been extracted from a middle portion of the regenerationtower.

According to a second aspect of the present invention, in the inventionaccording to the first aspect, the steam-condensate heat exchanger isinterposed in a rich-solution supply pipe for feeding a rich solutionfrom the absorption tower, and a flash drum is provided in either anupstream side or a downstream side of the steam-condensate heatexchanger.

According to a third aspect of the present invention, in the inventionaccording to the second aspect, the CO₂ recovery system further includesa branching node provided in the rich-solution supply pipe and dividinga rich solution; a steam-condensate heat exchanger that is provided in afirst rich-solution supply pipe, and heats the rich solution; a flashdrum provided in the downstream side of the steam-condensate heatexchanger; and a semi-lean-solution heat exchanger that is provided in asecond rich-solution supply pipe, and heats the rich solution withresidual heat of a semi-lean solution obtained by removing part of CO₂from the rich solution in the flash drum.

According to a fourth aspect of the present invention, in the inventionaccording to the first aspect, the CO₂ recovery system further includesa branching node provided in a rich-solution supply pipe and dividing arich solution; a steam-condensate heat exchanger that is provided in anend of a first rich-solution supply pipe, and flashes the rich solution;and a semi-lean-solution heat exchanger that is provided in a secondrich-solution supply pipe, and heats the rich solution with residualheat of a semi-lean solution obtained by removing part of CO₂ from therich solution in the steam-condensate heat exchanger. An end of asemi-lean-solution supply pipe for supplying the semi-lean solution isconnected to a middle stage portion of the absorption tower.

According to a fifth aspect of the present invention, in the inventionaccording to the fourth aspect, the steam-condensate heat exchanger thatflashes the rich solution includes a flash drum in which a flashportion, for flashing the rich solution, is provided in its upper side,a filling layer provided in the flash drum, and a steam supply unitprovided in a lower portion of the flash drum and supplying steamobtained from steam condensate.

According to a sixth aspect of the present invention, in the inventionaccording to the first aspect, the CO₂ recovery system further includesan upper-portion regeneration tower and a lower-portion regenerationtower obtained by dividing the regeneration tower into upper and lowerportions; a branching node provided in a rich-solution supply pipe anddividing a rich solution; a steam-condensate heat exchanger interposedin a first rich-solution supply pipe branched; and a semi-lean-solutionheat exchanger that is provided in a second rich-solution supply pipe,and heats the rich solution with residual heat of a semi-lean solutionobtained by removing part of CO₂ from the rich solution in theupper-portion regeneration tower. The first rich-solution supply pipe isconnected to the lower-portion regeneration tower, and an end of thesecond rich-solution supply pipe is connected to the upper-portionregeneration tower, and an end of a semi-lean-solution supply pipe forsupplying the semi-lean solution is connected to a middle stage portionof the absorption tower.

According to a seventh aspect of the present invention, in the inventionaccording to any one of first to sixth aspects, the CO₂ recovery systemfurther includes a lean-solution heat exchanger that is interposed in arich-solution supply pipe, and heats the rich solution with residualheat of a lean solution fed from the regeneration tower.

According to an eighth aspect of the present invention, in the inventionaccording to the first aspect, the CO₂ recovery system further includesan upper-portion regeneration tower, a middle-portion regenerationtower, and a lower-portion regeneration tower obtained by dividing theregeneration tower into upper, middle, and lower portions; a branchingnode provided in a rich-solution supply pipe and dividing a richsolution; a lean-solution heat exchanger interposed in a firstrich-solution supply pipe branched; a semi-lean-solution heat exchangerthat is provided in a second rich-solution supply pipe, and heats therich solution with residual heat of a semi-lean solution obtained byremoving part of CO₂ from the rich solution in the upper-portionregeneration tower; and a steam-condensate heat exchanger that extractsa semi-lean solution, obtained by removing part of CO₂ from the richsolution in the middle-portion regeneration tower, to the outside of theregeneration tower, and heats the semi-lean solution. An end of thefirst rich-solution supply pipe is connected to the middle-portionregeneration tower, and an end of a supply pipe for supplying thesemi-lean solution is connected to a middle stage portion of theabsorption tower.

According to a ninth aspect of the present invention, in the inventionaccording to the first aspect, the regeneration tower is divided into atleast two stages, and the CO₂ recovery system further includes asteam-condensate heat exchanger that heats a semi-lean solution obtainedby removing part of CO₂ from the rich solution, with residual heat ofthe steam condensate, the semi-lean solution having been extracted froman upper stage side of the regeneration tower divided, wherein thesemi-lean solution heated is supplied to a lower stage side of theregeneration tower.

According to a tenth aspect of the present invention, in the inventionaccording to the first aspect, the regeneration tower is divided into atleast two stages, and the CO₂ recovery system further includes asteam-condensate heat exchanger that heats a semi-lean solution obtainedby removing part of CO₂ from the rich solution, with residual heat ofthe steam condensate, the semi-lean solution having been extracted froman upper stage side of the regeneration tower divided; and alean-solution heat exchanger interposed in a rich-solution supply pipe,the lean-solution heat exchanger supplying the semi-lean solution heatedto a lower stage side of the regeneration tower and heating the richsolution with residual heat of the lean solution fed from theregeneration tower.

According to an eleventh aspect of the present invention, in theinvention according to the first aspect, the regeneration tower isdivided into at least two stages, and the CO₂ recovery system furtherincludes a steam-condensate heat exchanger that heats a semi-leansolution obtained by removing part of CO₂ from the rich solution, withresidual heat of the steam condensate, the semi-lean solution havingbeen extracted from an upper stage side of the regeneration towerdivided; a lean-solution heat exchanger interposed in a rich-solutionsupply pipe, the lean-solution heat exchanger supplying the semi-leansolution heated to a lower stage side of the regeneration tower andheating the rich solution with residual heat of the lean solution fedfrom the regeneration tower; a first branching node provided in therich-solution supply pipe and dividing the rich solution; a firstlean-solution heat exchanger interposed in a first rich-solution supplypipe branched at the first branching node; a semi-lean-solution heatexchanger that is provided in a second rich-solution supply pipebranched at the first branching node, and heats the rich solution withresidual heat of a semi-lean solution obtained by removing part of CO₂from the rich solution in the upper-portion regeneration tower; a secondlean-solution heat exchanger in which a joint solution joined betweenthe first rich-solution supply pipe and the second rich-solution supplypipe is heat-exchanged after heat exchange is performed in thesemi-lean-solution heat exchanger; a second branching node provided inthe downstream side of the semi-lean-solution heat exchanger; and asteam-condensate heat exchanger interposed in a first semi-lean-solutionsupply pipe branched at the second branching node. An end of the firstsemi-lean-solution supply pipe is connected to a lower stage side of theregeneration tower, and an end of a second semi-lean-solution supplypipe branched at the second branching node is connected to a middlestage portion of the absorption tower.

According to a twelfth aspect of the present invention, in the inventionaccording to the first aspect, the regeneration tower is divided into atleast two stages, and the CO2 recovery system further includes alean-solution heat exchanger that heats a semi-lean solution obtained byremoving part of CO2 from the rich solution, with residual heat of thelean solution fed from the regeneration tower, the semi-lean solutionhaving been extracted from an upper stage side of the regeneration towerdivided, wherein the lean solution heated is supplied to a lower stageside of the regeneration tower.

According to a thirteenth aspect of the present invention, in theinvention according to the first aspect, the CO2 recovery system furtherincludes a first lean-solution heat exchanger that heats a semi-leansolution obtained by removing part of CO2 from the rich solution, withresidual heat of the lean solution fed from the regeneration tower, thesemi-lean solution having been extracted from an upper stage side of theregeneration tower divided, and the first lean-solution heat exchangerbeing arranged next to a steam-condensate heat exchanger; and a secondlean-solution heat exchanger that is provided in a rich-solution supplypipe and heats the rich solution with residual heat of the lean solutionobtained after the semi-lean solution is heated.

According to a fourteenth aspect of the present invention, in theinvention according to the first aspect, the CO2 recovery system furtherincludes an upper-portion regeneration tower, a middle-portionregeneration tower, and a lower-portion regeneration tower obtained bydividing the regeneration tower into upper, middle, and lower portions;a first lean-solution heat exchanger that heats a semi-lean solutionobtained by removing part of CO2 from the rich solution, with the leansolution fed from the regeneration tower, the semi-lean solution havingbeen extracted from the upper-portion regeneration tower; a firststeam-condensate heat exchanger that heats a semi-lean solution obtainedby removing part of CO2 from the rich solution, with the steamcondensate, the semi-lean solution having been extracted from themiddle-portion regeneration tower; a semi-lean-solution heat exchangerthat is provided in a rich-solution supply pipe, and heats the richsolution with the part of the semi-lean solution extracted from themiddle-portion regeneration tower; and a second lean-solution heatexchanger that is provided in the downstream side of thesemi-lean-solution heat exchanger in the rich-solution supply pipe, andheats the rich solution with residual heat of the lean solution obtainedafter the semi-lean solution is heated. The semi-lean solutionrespectively heated is supplied to the lower stage side in theregeneration tower, and the semi-lean solution, after beingheat-exchanged in the semi-lean-solution heat exchanger, is supplied toa middle stage portion of the absorption tower.

According to a fifteenth aspect of the present invention, in theinvention according to any one of the fourth, fifth, eighth, eleventh,and fourteenth aspects, the absorption tower is divided into two stages:upper and lower stages, and the semi-lean solution to be supplied to amiddle stage portion of the absorption tower is jointed with a semi-leansolution extracted from the upper-stage absorption tower, to be suppliedto the lower-stage absorption tower.

A sixteenth aspect of the present invention relates to a CO2 recoverysystem including an absorption tower that contacts CO2-containing gaswith a CO2-absorbing solution to remove CO2 and a regeneration towerthat regenerates a rich solution having absorbed CO2, and reusing a leansolution, obtained by removing CO2 from the rich solution in theregeneration tower, in the absorption tower, a regeneration heater thatheat-exchanges a solution recovered to a bottom portion of theregeneration tower with saturated steam; and a steam-condensate heatexchanger that heats the rich solution with residual heat of steamcondensate.

A seventeenth aspect of the present invention relates to a CO2 recoverysystem including an absorption tower that contacts CO2-containing gaswith a CO2-absorbing solution to remove CO2 and a regeneration towerthat regenerates a rich solution having absorbed CO2, and reusing a leansolution, obtained by removing CO2 from the rich solution in theregeneration tower, in the absorption tower, a regeneration heater thatheat-exchanges a solution recovered to a bottom portion of theregeneration tower with saturated steam; and a steam-condensate heatexchanger that heats a semi-lean solution, obtained by removing part ofCO2 from the lean solution, with residual heat of steam condensate, thesemi-lean solution having been extracted from a middle portion of theregeneration tower.

A eighteenth aspect of the present invention relates to a CO2 recoverysystem including an absorption tower that contacts CO2-containing gaswith a CO2-absorbing solution to remove CO2 and a regeneration towerthat regenerates a rich solution having absorbed CO2, and reusing a leansolution, obtained by removing CO2 from the rich solution in theregeneration tower, in the absorption tower, a lean-solution heatexchanger that heats a semi-lean solution, obtained by removing part ofCO2 from the rich solution, with residual heat of a lean solution, thesemi-lean solution having been extracted from a middle portion of theregeneration tower.

A nineteenth aspect of the present invention relates to a CO2 recoverymethod including contacting CO2-containing gas with a CO2 absorbingsolution in an absorption tower to remove CO2, regenerating a richsolution having absorbed CO2 in a regeneration tower, and reusing a leansolution, regenerated by removing CO2 from the rich solution, in theabsorption tower, heat-exchanging a solution recovered to a bottomportion of the regeneration tower with steam; and heating the richsolution with residual heat of steam condensate.

A twentieth aspect of the present invention relates to a CO2 recoverymethod including contacting CO2-containing gas with a CO2 absorbingsolution in an absorption tower to remove CO2, regenerating a richsolution having absorbed CO2 in a regeneration tower, and reusing a leansolution, regenerated by removing CO2 from the rich solution, in theabsorption tower, heat-exchanging a solution recovered to a bottomportion of the regeneration tower with steam; and heating a semi-leansolution obtained by removing part of CO2 from the rich solution, withresidual heat of steam condensate, the semi-lean solution having beenextracted from a middle portion of the regeneration tower.

A twenty-first aspect of the present invention relates to a CO2 recoverymethod including contacting CO2-containing gas with a CO2 absorbingsolution in an absorption tower to remove CO2, regenerating a richsolution having absorbed CO2 in a regeneration tower, and reusing a leansolution, regenerated by removing CO2 from the rich solution, in theabsorption tower, heating a semi-lean solution obtained by removing partof CO2 from the rich solution, with residual heat of a lean solution,the semi-lean solution having been extracted from a middle portion ofthe regeneration tower.

Effect of the Invention

According to the present invention, it is possible to provide a CO2recovery system and method in which energy saving is achieved by usingresidual heat of steam condensate.

Furthermore, it is possible to provide a CO2 recovery system and methodwith improved energy efficiency by heating a semi-lean solution withresidual heat of a lean solution, the semi-lean solution obtained byremoving part of CO2 from a rich solution and extracted from the middleof the regeneration tower when the rich solution having absorbed CO2 isregenerated in the regeneration tower.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic of a CO2 recovery system according to a firstembodiment;

FIG. 2 is a schematic of a CO2 recovery system according to a secondembodiment;

FIG. 3 is a schematic of a CO2 recovery system according to a thirdembodiment;

FIG. 4 is a schematic of a CO2 recovery system according to a fourthembodiment;

FIG. 5 is a schematic of a CO2 recovery system according to a fifthembodiment;

FIG. 6 is a schematic of a CO2 recovery system according to a sixthembodiment;

FIG. 7 is a schematic of a CO2 recovery system according to a seventhembodiment;

FIG. 8 is a schematic of a CO2 recovery system according to a eighthembodiment;

FIG. 9 is a schematic of a CO2 recovery system according to a ninthembodiment;

FIG. 10 is a schematic of a CO2 recovery system according to example 1;

FIG. 11 is a schematic of a CO2 recovery system according to example 2;

FIG. 12 is a schematic of a CO2 recovery system according to example 3;

FIG. 13 is a schematic of a CO2 recovery system according to example 4;

FIG. 14 is a schematic of a CO2 recovery system according to example 5;

FIG. 15 is a schematic of a CO2 recovery system according to example 6;

FIG. 16 is a schematic of a CO2 recovery system according to example 7;

FIG. 17 is a schematic of a CO2 recovery system according to example 8;

FIG. 18 is a schematic of a CO2 recovery system according to example 9;

FIG. 19 is a schematic of a CO2 recovery system according to example 10;

FIG. 20 is a schematic of a CO2 recovery system according to example 11;

FIG. 21 is a schematic of a CO2 recovery system according to example 12;and

FIG. 22 is a schematic of a CO2 recovery system according to aconventional example.

EXPLANATIONS OF LETTERS OR NUMERALS

11 CO2-containing gas

12 CO2-absorbing solution

13 Absorption tower

14 Rich solution

15 Regeneration tower

16 Lean solution

17 Steam

18 Regeneration heater

19 Steam condensate

21 Steam-condensate heat exchanger

22 Lean-solution supply pipe

23 Lean-solution heat exchanger

8 Nozzle

9 Chimney tray

10 CO2-removed exhaust gas

Best(S) Mode for Carrying Out the Invention

The present invention is explained in detail below with reference to theattached drawings. It is noted that the present invention is not limitedby its exemplary embodiments and examples. It is also noted thatcomponents in the following embodiments and examples contain thosepersons skilled in the art can easily think of or those substantiallyequivalent thereto.

The embodiments of the present invention are explained first, and theexemplary examples are explained in detail next.

[First Embodiment]

FIG. 1 is a schematic of a CO2 recovery system according to a firstembodiment.

As shown in FIG. 1, the CO2 recovery system according to the firstembodiment of the present invention includes an absorption tower 13 thatmakes CO2-containing gas 11 containing CO2 to contact with aCO2-absorbing solution 12 to produce a CO2-rich solution 14; and aregeneration tower 15 that regenerates a rich solution 14 to produce alean solution (regenerated solution) 16. The regenerated solution 16 isreused in the absorption tower 13. The CO2 recovery system includes aregeneration heater 18 that implements heat exchange between the leansolution 16, which accumulates near the bottom of the regeneration tower15, and high temperature steam 17; a rich-solution supply pipe 20 whichsupplies the rich solution 14 from the absorption tower 13 to theregeneration tower 15; a steam-condensate heat exchanger 21 that isprovided in rich-solution supply pipe 20 and heats the rich solution 14with the residual heat of steam condensate 19 fed from the regenerationheater 18.

In the first embodiment, the lean solution 16 being the regeneratedsolution is supplied from the regeneration tower 15 to the absorptiontower 13 through a lean-solution supply pipe 22. A lean-solution heatexchanger 23, which heats the rich solution 14 with residual heat of thelean solution 16, is provided in the rich-solution supply pipe 20.

In FIG. 1, reference numeral 8 represents a nozzle, 9 a chimney tray, 10CO2-removed exhaust gas, 25 a and 25 b filling layers provided in theabsorption tower 13, and 26 a and 26 b filling layers provided in theregeneration tower 15.

The heat exchanger used in the first embodiment is not particularlylimited. In other words, a known heat exchanger such as a plate heatexchanger and a shell and tube heat exchanger can be used.

The CO2-absorbing solution used in the present invention is notparticularly limited. For example, an alkanolamine and a hindered aminegroup having alkanolamine and alcoholic hydroxyl can be exemplified. Thealkanolamine can be exemplified by monoethanolamine, diethanolamine,triethanolamine, methyldiethanolamine, diisopropanolamine,diglycolamine, and the like, but generally, monoethanolamine (MEA) ispreferably used. The hindered amine having alcoholic hydroxyl can beexemplified by 2-amino-2-methyl-1-propanol(AMP),2-(ethylamino)-ethanol(EAE), 2-(methylamino)-ethanol(MAE), and2-(diethylamino)-ethanol(DEAE).

Thus, there is provided the steam-condensate heat exchanger 21 thatheats the rich solution 14 with the residual heat of the steamcondensate 19 fed from the regeneration heater 18. Thus, the residualheat of the steam condensate 19 can be effectively used to raise thesupply temperature of the rich solution 14 to be supplied to theregeneration tower 15, so that reduction in the supply amount of steamused in the regeneration tower 15 can be achieved.

The CO2-containing gas 11 to be supplied to a CO2 recovery device isfirst cooled by a cooling device (not shown) to about 40° C. to 50° C.and supplied to the CO2 recovery device. On the other hand, the leansolution 16 which is the absorbing solution 12 regenerated is cooled toabout 40° C. by a cooling device (not shown).

The rich solution 14 output from the absorption tower 13 of the CO2removal device is sent toward the regeneration tower 15 at about 50° C.due to heat reaction. The rich solution 14 is then heated up to about110° C. in the lean-solution heat exchanger 23 and supplied to theregeneration tower 15. However, by providing the steam-condensate heatexchanger 21 in which the rich solution 14 is heat-exchanged with theheat (e.g., 137° C.) of the steam condensate 19, the temperature of therich solution 14 can be increased by several degrees.

In the configuration of FIG. 1, a flash drum for causing the richsolution to flash can be provided in either one of an upstream side anda downstream side of the steam-condensate heat exchanger 21, and theflash drum can be made to discharge CO2 contained in the rich solutionin the outside of the regeneration tower. According to suchconfiguration, part of CO2 in the rich solution 14 to be regenerated inthe regeneration tower 15 is previously removed by the flash drum, andit becomes possible to reduce the supply amount of steam to be used forCO2 removal in the regeneration tower 15.

[Second Embodiment]

FIG. 2 is a schematic of a CO2 recovery system according to a secondembodiment.

Components the same as those of the CO2 recovery system according to thefirst embodiment are assigned with the same reference numerals, andexplanation thereof is omitted.

As shown in FIG. 2, the CO2 recovery system according to the secondembodiment of the present invention further includes, in addition to theconfiguration of the first embodiment, a branching node 24 provided inthe rich-solution supply pipe 20 that branches the rich solution 14 intothe first rich-solution supply pipe 20-1 and the second rich-solutionsupply pipe 20-2; the steam-condensate heat exchanger 21 that isprovided in the first rich-solution supply pipe 20-1 and heats the richsolution 14; a flash drum 27 provided in the downstream side of thesteam-condensate heat exchanger 21; and a semi-lean-solution heatexchanger 29 that is provided in the second rich-solution supply pipe20-2 and heats the rich solution 14 with the residual heat of asemi-lean solution 28 obtained by removing part of CO₂ from the richsolution in the flash drum 27. An end of a semi-lean-solution supplypipe 30 for supplying the semi-lean solution 28 is connected to a middlestage portion of the absorption tower 13. The second rich-solutionsupply pipe 20-2 is connected near the upper stage of the regenerationtower 15, and CO₂ is removed and recovered in the regeneration tower 15.

Thus, the steam-condensate heat exchanger 21 heats the rich solution 14with the residual heat of the steam condensate 19 fed from theregeneration heater 18, in which the rich solution is heated with theresidual heat of the steam condensate. therefore, the residual heat ofthe steam condensate 19 having been used in the regeneration heater 18is effectively used. The rich solution 14 heated with the residual heatis introduced into the flash drum 27. Then, the rich solution 14 iscaused to flash in the flash drum 27 to enable improvement of CO₂removal efficiency. Moreover, the rich solution 14 is heat-exchangedwith the residual heat of the semi-lean solution 28 obtained by removingpart of CO₂ from the rich solution and fed from the flash drum 27, inthe semi-lean-solution heat exchanger 29 interposed in the secondrich-solution supply pipe 20-2 branched. Therefore, it is possible toincrease the temperature of the rich solution 14 to be introduced intothe regeneration tower 15, and as a result, the supply amount of steamto be used in the regeneration tower 15 can be reduced. Most of CO₂ isremoved from the semi-lean solution 28, obtained by removing part of CO₂from the rich solution, in the flash drum 27. Therefore, by supplyingthis semi-lean solution 28 to the middle stage portion of the absorptiontower 13, CO₂ is absorbed without being regenerated in the regenerationtower 15.

Furthermore, CO₂ removed in the flash drum 27 joins CO₂ fed from theregeneration tower 15, to be recovered separately.

The ratio of division of the rich solution 14 into the firstrich-solution supply pipe 20-1 and the second rich-solution supply pipe20-2 at the branching node 24 is simply set to a range from 30:70 to70:30, preferably 50:50.

The second embodiment is configured to further divide the inner side ofthe absorption tower 13 into two stages: an upper-stage filling layer13-U and a lower-stage filling layer 13-L; to extract the absorbingsolution 12 having absorbed CO₂, from the upper-stage filling layer 13-Uto the outside; and to mix the absorbing solution 12 with the semi-leansolution 28 to be cooled. This is because it is preferable to decreasethe temperature of a solution to be supplied because the absorptionreaction is an exothermic reaction. In this embodiment, the temperatureis decreased to about 40° C. to 50° C.

[Third Embodiment]

FIG. 3 is a schematic of a CO₂ recovery system according to a thirdembodiment.

Components the same as those in each of the CO₂ recovery systemsaccording to the first and the second embodiments are assigned with thesame reference numerals, and explanation thereof is omitted.

As shown in FIG. 3, the CO₂ recovery system according to the thirdembodiment of the present invention further includes, in addition to theconfiguration of the first embodiment, the branching node 24 provided inthe rich-solution supply pipe 20 and divides the rich solution 14 intothe first rich-solution supply pipe 20-1 and the second rich-solutionsupply pipe 20-2; a steam-condensate heat exchanger 31 that is providedin an end of the first rich-solution supply pipe 20-1 and causes therich solution 14 to flash; and the semi-lean-solution heat exchanger 29that is provided in the second rich-solution supply pipe 20-2 and heatsthe rich solution 14 with the residual heat of the semi-lean solution 28obtained by removing part of CO₂ from the rich solution in thesteam-condensate heat exchanger 31. And the end of thesemi-lean-solution supply pipe 30 for supplying the semi-lean solution28 is connected to the middle stage portion of the absorption tower 13.

In the third embodiment, the steam-condensate heat exchanger 31 is notan exchanger such as the plate heat exchanger, but includes, as shown inFIG. 3, a first flash drum 33 in which a flash portion 32, for causingthe rich solution 14 to flash, is provided in its upper side; a fillinglayer 34 provided in the first flash drum 33; and a steam supply portion36 that is provided in the lower-portion of the flash drum and suppliessteam 35 from the steam condensate 19.

If the steam condensate 19 is pressurized saturated steam, a secondflash drum 37 is provided to make it as atmospheric pressure steam 35,and the steam 35 is supplied to the first flash drum 33, where CO₂ isremoved from the rich solution 14 using the heat of the steam 35.

The semi-lean-solution heat exchanger 29 heats the rich solution 14using the residual heat of the semi-lean solution 28 obtained byremoving part of CO₂ from the rich solution in the first flash drum 33,and then, the rich solution is supplied to the middle stage portion ofthe absorption tower 13.

Thus, the steam-condensate heat exchanger 31 heats the rich solution 14in the first rich-solution supply pipe 20-1, with the residual heat ofthe steam condensate 19 fed from the regeneration heater 18, in whichthe rich solution is heated with the steam 35. Therefore, the residualheat of the steam condensate 19 having been used in the regenerationheater 18 is effectively used. The rich solution 14 is heat-exchangedusing the residual heat of the semi-lean solution 28 obtained byremoving CO₂ by flash in the steam-condensate heat exchanger 31, in thesemi-lean-solution heat exchanger 29 interposed in the secondrich-solution supply pipe 20-2 branched. Therefore, it is possible toincrease the temperature of the rich solution 14 to be introduced intothe regeneration tower 15, and as a result, the supply amount of steamto be used in the regeneration tower 15 can be reduced.

Furthermore, CO₂ removed in the first flash drum 33 joins CO₂ fed fromthe regeneration tower 15, to be recovered separately.

The first flash drum 33 functions as an auxiliary regeneration tower forthe regeneration tower 15.

[Fourth Embodiment]

FIG. 4 is a schematic of a CO₂ recovery system according to a fourthembodiment.

Components the same as those in each of the CO₂ recovery systemsaccording to the first to the third embodiments are assigned with thesame reference numerals, and explanation thereof is omitted.

As shown in FIG. 4, the CO₂ recovery system according to the fourthembodiment of the present invention further includes, in addition to theconfiguration of the first embodiment, an upper-portion regenerationtower 15-U and a lower-portion regeneration tower 15-L into which theinner side of the regeneration tower 15 is vertically divided; thebranching node 24 provided in the rich-solution supply pipe 20 anddividing the rich solution 14; the steam-condensate heat exchanger 21interposed in the first rich-solution supply pipe 20-1 branched; and thesemi-lean-solution heat exchanger 29 that is provided in the secondrich-solution supply pipe 20-2, and heats the rich solution 14 with theresidual heat of the semi-lean solution 28 obtained by removing part ofCO₂ from the rich solution in the upper-portion regeneration tower 15-U.And, the end of the first rich-solution supply pipe 20-1 is connected tothe lower-portion regeneration tower 15-L, the end of the secondrich-solution supply pipe 20-2 is connected to the upper-portionregeneration tower 15-U, and the end of the semi-lean-solution supplypipe 30 for supplying the semi-lean solution 28 is connected to themiddle stage portion of the absorption tower 13.

The fourth embodiment is configured to provide the steam-condensate heatexchanger 21 that heats the rich solution 14 with the residual heat ofthe steam condensate 19 fed from the regeneration heater 18, in whichthe rich solution is heated with the residual heat of the steamcondensate. Therefore, the residual heat of the steam condensate 19having been used in the regeneration heater 18 is effectively used.Furthermore, the rich solution 14 heated with the residual heat isintroduced into the lower-portion regeneration tower 15-L, where it isregenerated.

The semi-lean solution 28, obtained by removing part of CO₂ from therich solution 14 in the upper-portion regeneration tower 15-U, isextracted to the outside through the semi-lean-solution supply pipe 30,and the rich solution 14 is heat-exchanged with the residual heat of thesemi-lean solution in the semi-lean-solution heat exchanger 29interposed in the second rich-solution supply pipe 20-2 branched.Therefore, it is possible to increase the temperature of the richsolution 14 to be introduced into the regeneration tower 15, and as aresult, the supply amount of steam to be used in the regeneration tower15 can be reduced.

The ratio of division of the rich solution 14 into the firstrich-solution supply pipe 20-1 and the second rich-solution supply pipe20-2 at the branching node 24 is simply set to a range from 25:75 to75:25.

[Fifth Embodiment]

FIG. 5 is a schematic of a CO₂ recovery system according to a fifthembodiment.

Components the same as those in each of the CO₂ recovery systemsaccording to the first to the fourth embodiments are assigned with thesame reference numerals, and explanation thereof is omitted.

As shown in FIG. 5, the CO₂ recovery system according to the fifthembodiment of the present invention includes the upper-portionregeneration tower 15-U, a middle-portion regeneration tower 15-M, andthe lower-portion regeneration tower 15-L, which are obtained bydividing the regeneration tower 15 into three: upper, middle, and lowerportions; the branching node 24 provided in the rich-solution supplypipe 20 and dividing the rich solution 14; the lean-solution heatexchanger 23 interposed in the first rich-solution supply pipe 20-1branched; the semi-lean-solution heat exchanger 29 that is provided inthe second rich-solution supply pipe 20-2, and heats the rich solutionwith the residual heat of the semi-lean solution 28 obtained by removingpart of CO₂ from the rich solution in the upper-portion regenerationtower 15-U; and the steam-condensate heat exchanger 21 that extracts thesemi-lean solution 28 obtained by removing part of CO₂ from the richsolution in the middle-portion regeneration tower 15-M, to the outsideof the regeneration tower through an extraction pipe 41, and that heatsthe semi-lean solution 28 with the residual heat of the steam condensate19. And, the end of the first rich-solution supply pipe 20-1 isconnected to the middle-portion regeneration tower 15-M, the end of thesecond rich-solution supply pipe 20-2 is connected to the upper-portionregeneration tower 15-U, the extraction pipe 41 is connected to thelower-portion regeneration tower 15-L, and the end of the supply pipe 30for supplying the semi-lean solution 28 is connected to the middle stageportion of the absorption tower 13.

The fifth embodiment is configured to provide the steam-condensate heatexchanger 21 that heats the semi-lean solution 28 extracted through theextraction pipe 41, in which the semi-lean solution 28 is heated withthe residual heat of the steam condensate 19. Therefore, the residualheat of the steam condensate 19 having been used in the regenerationheater 18 is effectively used, and as a result, the supply amount ofsteam to be used in the regeneration tower 15 can be reduced.

Furthermore, the rich solution 14 is heat-exchanged, using the leansolution 16 regenerated in the regeneration tower 15, in thelean-solution heat exchanger 23 interposed in the first rich-solutionsupply pipe 20-1, and the rich solution 14 heated with the residual heatis introduced into the middle-portion regeneration tower 15-M, whichallows reduction in the supply amount of steam to be used in theregeneration tower.

The semi-lean solution 28, obtained by removing part of CO2 from therich solution in the upper-portion regeneration tower 15-U, is extractedto the outside through the semi-lean-solution supply pipe 30, and therich solution 14 is heat-exchanged with the residual heat of thesemi-lean solution 28 in the semi-lean-solution heat exchanger 29interposed in the second rich-solution supply pipe 20-2 branched.Therefore, it is possible to increase the temperature of the richsolution 14 to be introduced into the upper-portion regeneration tower15-U, and as a result, the supply amount of steam to be used in theregeneration tower 15 can be reduced.

The ratio of division of the rich solution 14 into the firstrich-solution supply pipe 20-1 and the second rich-solution supply pipe20-2 at the branching node 24 is simply set to a range from 25:75 to75:25.

[Sixth Embodiment]

FIG. 6 is a schematic of a CO2 recovery system according to a sixthembodiment.

Components the same as those in each of the CO2 recovery systemsaccording to the first to the fifth embodiments are assigned with thesame reference numerals, and explanation thereof is omitted.

As shown in FIG. 6, the CO2 recovery system according to the sixthembodiment of the present invention includes the upper-portionregeneration tower 15-U and the lower-portion regeneration tower 15-L,which are obtained by dividing the regeneration tower at least into twoportions; and the steam-condensate heat exchanger 21 that heats thesemi-lean solution 28, obtained by removing part of CO2 from the richsolution, with the residual heat of the steam condensate, the semi-leansolution 28 having been extracted from the upper-portion regenerationtower 15-U through the extraction pipe 41. And the semi-lean solution 28heated is supplied to the lower-portion regeneration tower 15-L.

The sixth embodiment is configured to provide the steam-condensate heatexchanger 21 that heats the semi-lean solution 28 extracted through theextraction pipe 41, with the residual heat of the steam condensate 19fed from the regeneration heater 18, in which the semi-lean solution 28is heated with the residual heat of the steam condensate. Therefore, theresidual heat of the steam condensate 19 having been used in theregeneration heater 18 is effectively used, and as a result, the supplyamount of steam to be used in the regeneration tower 15 can be reduced.

[Seventh Embodiment]

FIG. 7 is a schematic of a CO2 recovery system according to a seventhembodiment.

Components the same as those in each of the CO2 recovery systemsaccording to the first to the sixth embodiments are assigned with thesame reference numerals, and explanation thereof is omitted.

As shown in FIG. 7, the CO2 recovery system according to the seventhembodiment of the present invention includes, in addition to the systemof the sixth embodiment, a first branching node 24-1 provided in therich-solution supply pipe 20 and dividing the rich solution 14; a firstlean-solution heat exchanger 23-1 interposed in the first rich-solutionsupply pipe 20-1 branched at the first branching node 24-1; thesemi-lean-solution heat exchanger 29 that is provided in the secondrich-solution supply pipe 20-2 branched at the first branching node24-1, and heats the rich solution 14 with the residual heat of thesemi-lean solution 28 obtained by removing part of CO2 from the richsolution in the upper-portion regeneration tower 15-U; a secondlean-solution heat exchanger 23-2 in which the rich solution 14 joinedat a joint 42 between the first rich-solution supply pipe 20-1 and thesecond rich-solution supply pipe 20-2, is heat-exchanged after the heatexchange in the semi-lean-solution heat exchanger 29; a second branchingnode 24-2 provided in the downstream side of the semi-lean-solution heatexchanger 29 provided in the supply pipe 30 for supplying the semi-leansolution 28; and the steam-condensate heat exchanger 21 interposed in afirst semi-lean-solution supply pipe 30-1 branched at the secondbranching node 24-2. And the end of the first semi-lean-solution supplypipe 30-1 is connected to the lower-portion regeneration tower 15-L, andthe end of a second semi-lean-solution supply pipe 30-2 branched at thesecond branching node 24-2 is connected to the middle stage portion ofthe absorption tower 13.

In the seventh embodiment, the semi-lean-solution heat exchanger 29 usesthe residual heat of the semi-lean solution 28 extracted from theupper-portion regeneration tower 15-U to heat the rich solution 14, andthe residual heat of the semi-lean solution 28 is thereby effectivelyused. Moreover, because the steam-condensate heat exchanger 21 isprovided in the way in which part of the semi-lean solution 28 isreturned again to the lower-portion regeneration tower 15-L through thefirst semi-lean-solution supply pipe 30-1, the semi-lean solution 28 canbe heated with the residual heat of the steam condensate 19. Theresidual heat of the steam condensate 19 having been used in theregeneration heater 18 is thereby effectively used, and as a result, thesupply amount of steam to be used in the regeneration tower 15 can bereduced.

One part of the rich solution 14 once divided is heat-exchanged in thesemi-lean-solution heat exchanger 29, and the other part of the richsolution 14 divided is also heat-exchanged in the first lean-solutionheat exchanger 23-1, and these parts of the rich solution 14 are jointedat the joint 42, and are further heat-exchanged in the secondlean-solution heat exchanger 23-2, to be supplied to the upper-portionregeneration tower 15-U. The temperature of the rich solution 14 to beintroduced into the regeneration tower thereby increases, and as aresult, the supply amount of steam to be used in the regeneration tower15 can be reduced.

[Eighth Embodiment]

FIG. 8 is a schematic of a CO2 recovery system according to an eighthembodiment.

Components the same as those in each of the CO2 recovery systemsaccording to the first to the seventh embodiments are assigned with thesame reference numerals, and explanation thereof is omitted.

As shown in FIG. 8, the CO2 recovery system according to the eighthembodiment of the present invention includes the upper-portionregeneration tower 15-U and the lower-portion regeneration tower 15-L,which are obtained by dividing the regeneration tower at least into twoportions; the first lean-solution heat exchanger 23-1 that is interposedin the extraction pipe 41 for extracting the semi-lean solution 28,obtained by removing part of CO2 from the rich solution, from theupper-portion regeneration tower 15-U divided, and heats the semi-leansolution 28 with the residual heat of the lean solution 16 that flowsthrough the lean-solution supply pipe 22; and the steam-condensate heatexchanger 21 that is provided in the downstream side of and adjacent tothe first lean-solution heat exchanger 23-1 in the extraction pipe 41,and reheats the semi-lean solution 28 having been heated once, with thesteam condensate 19. And the second lean-solution heat exchanger 23-2,which heats the rich solution 14 with the residual heat of the leansolution after the semi-lean solution 28 is heated, is provided in therich-solution supply pipe 20.

In the eighth embodiment, the semi-lean solution 28 extracted from theupper-portion regeneration tower 15-U is heated in the firstlean-solution heat exchanger 23-1, and further heated in thesteam-condensate heat exchanger 21, and the residual heat of the steamcondensate 19 having been used in the regeneration heater 18 is therebyeffectively used. As a result, the supply amount of steam to be used inthe regeneration tower 15 can be reduced.

Furthermore, when the inside of the regeneration tower is divided into aplurality of stages and the semi-lean solution 28, extracted from eachstage of the regeneration tower divided, is returned to the regenerationtower on the lower stage side, the semi-lean solution 28 isheat-exchanged in the lean-solution heat exchanger and thesteam-condensate heat exchanger respectively. This causes thetemperature of the semi-lean solution 28, which is regenerated in theregeneration tower 15, to be increased, and consequently, the supplyamount of steam to be used in the regeneration tower 15 can be reduced.

[Ninth Embodiment]

FIG. 9 is a schematic of a CO2 recovery system according to a ninthembodiment.

Components the same as those in each of the CO2 recovery systemsaccording to the first to the eighth embodiments are assigned with thesame reference numerals, and explanation thereof is omitted.

As shown in FIG. 9, the CO2 recovery system according to the ninthembodiment of the present invention includes the upper-portionregeneration tower 15-U, the middle-portion regeneration tower 15-M, andthe lower-portion regeneration tower 15-L, which are obtained bydividing the regeneration tower 15 into three: upper, middle, and lowerportions; the first lean-solution heat exchanger 23-1 that heats thesemi-lean solution 28, obtained by removing part of CO2 from the richsolution and extracted from the upper-portion regeneration tower 15-Uthrough a first extraction pipe 41-1, with the lean solution fed fromthe regeneration tower; the steam-condensate heat exchanger 21 thatheats the semi-lean solution 28, obtained by removing part of CO2 fromthe rich solution and extracted from the middle-portion regenerationtower 15-M through a second extraction pipe 41-2, with the steamcondensate; the semi-lean-solution heat exchanger 29 that is provided inthe rich-solution supply pipe 20, and heats the rich solution 14 withthe part of the semi-lean solution 28 extracted from the middle-portionregeneration tower 15-M; and the second lean-solution heat exchanger23-2 that is provided in the downstream side of the semi-lean-solutionheat exchanger 29 in the rich-solution supply pipe 20, and heats therich solution 14 with the residual heat of the lean solution 16 afterthe semi-lean solution 28 is heated. And the semi-lean solution heatedis supplied to the lower stage side of the regeneration tower, and thesemi-lean solution 28 after heat exchange is performed in thesemi-lean-solution heat exchanger 29 is supplied to the middle stageportion of the absorption tower 13 through the semi-lean-solution supplypipe 30.

In the ninth embodiment, the semi-lean solution 28 respectivelyextracted from the upper-portion regeneration tower 15-U and themiddle-portion regeneration tower 15-M is heated in the firstlean-solution heat exchanger 23-1 or in the steam-condensate heatexchanger 21, and the residual heat of the lean solution 16 and of thesteam condensate 19 is thereby effectively used. As a result, the supplyamount of steam to be used in the regeneration tower 15 can be reduced.

The residual heat of the semi-lean solution 28 after heat exchange isperformed in the steam-condensate heat exchanger 21 is used for heatingthe rich solution, and the residual heat of the lean solutionheat-exchanged in the first lean-solution heat exchanger 23-1 is usedfor heating the rich solution in the second lean-solution heat exchanger23-2. It is thereby possible to increase the temperature of the richsolution 14 to be supplied to the regeneration tower 15, and as aresult, the supply amount of steam to be used in the regeneration tower15 can be reduced.

The exemplary examples indicating the effect of the present inventionare explained below, but the present invention is not limited by theexamples.

EXAMPLE 1

A CO2 recovery system according to example 1 of the present invention isexplained below with reference to the following drawing.

FIG. 10 is a schematic of the CO2 recovery system according to example1.

As shown in FIG. 10, the CO2-containing exhaust gas 11 supplied to theCO2 absorption tower 13 is brought into countercurrent contact with theabsorbing solution 12 in a filling portion, the absorbing solution 12having predetermined concentration and being supplied from the nozzle 8.CO2 in the combustion exhaust gas is absorbed and removed by theCO2-absorbing solution 12, and the remaining CO2-removed exhaust gas 10,from which CO2 has been absorbed and removed, is fed to the outside. Theabsorbing solution 12 supplied to the CO2 absorption tower 13 absorbsCO2, and reaction heat due to the absorption causes the temperature ofthe absorbing solution 12 to become higher than normal temperature in atower head. The absorbing solution having absorbed CO2 is sent by adischarge pump 51 for the absorbing solution, as the rich solution 14,to the lean-solution heat exchanger 23 and the steam-condensate heatexchanger 21, where it is heated, to be introduced into the regenerationtower 15.

In the regeneration tower 15, the absorbing solution is regenerated bybeing heated with the steam 17 by the regeneration heater 18, cooled asthe lean solution 16 by the lean-solution heat exchanger 23 and a cooler52 provided as necessary, and is returned to the CO2 absorption tower13. In the upper portion of the regeneration tower 15, CO2 separatedfrom the absorbing solution is cooled by a regeneration-tower refluxcondenser 53, the steam associated with CO2 is separated from condensedreflux water in a CO2 separator 54, and output to the outside of thesystem through a recovered-CO2 discharge line 55. Reflux water 56 isflowed back to the regeneration tower 15 by a reflux pump 57.

In the example 1, the steam used in the regeneration heater 18 isintroduced into a separator to be flashed, and the residual heat of thesteam flashed as the steam condensate 19 is used for heating the richsolution 14 in the steam-condensate heat exchanger 21.

As a comparison, the case where the steam-condensate heat exchanger 21is not provided is shown in FIG. 22.

If the temperature of the rich solution 14 to be discharged from theabsorption tower 13 was 50.5° C., the temperature was 114.2° C. whenonly the lean-solution heat exchanger 23 was provided, while in theexample 1, the steam-condensate heat exchanger 21 was provided, and thetemperature thereby increased to 116.7° C., consequently, the amount ofsteam consumed in the regeneration tower 15 became 97.96 MMkcal/h.

In FIG. 10, temperature (° C.) is surrounded by a rectangle, flow rate(t/h) is surrounded by a parallelogram, and the amount of heat(MMkcal/h) is represented with angled brackets. The same goes for FIG.11 to FIG. 21.

The amount of steam consumed in the comparative example of FIG. 22 was98.77 MMkcal/h. Assuming the comparative example is 100, the amount ofsteam consumed in this example becomes 99.2%. Therefore, the reductionrate of specific steam consumption (improvement effect) was 0.8%.

EXAMPLE 2

A CO2 recovery system according to example 2 of the present invention isexplained below with reference to the following drawing.

FIG. 11 is a schematic of the CO2 recovery system according to example2. Components the same as those of example 1 are assigned with the samereference numerals and explanation thereof is omitted.

In example 2, a flash drum 61 is provided in the downstream side of thesteam-condensate heat exchanger 21 that heats the rich solution 14. Inthe upstream side of the flash drum 61, the rich solution 14 is heatedin the steam-condensate heat exchanger 21, and therefore, CO2 in therich solution 14 can be removed in the flash drum 61.

The temperature of the rich solution fed from the flash drum 61 is103.9° C., but because part of CO2 has been removed, decreasing inlettemperature of the regeneration tower 15 causes the steam dischargedfrom the tower head to be reduced, which is preferable.

In example 2, as the result, the amount of steam consumed in theregeneration tower 15 became 97.64 MMkcal/h. Assuming the comparativeexample is 100, the amount of steam consumed in this example becomes98.9%. Therefore, the reduction rate of specific steam consumption(improvement effect) was 1.1%.

EXAMPLE 3

A CO2 recovery system according to example 3 of the present invention isexplained below with reference to the following drawing.

FIG. 12 is a schematic of the CO2 recovery system according to example3. Components the same as those of example 1 are assigned with the samereference numerals and explanation thereof is omitted.

In example 3, the flash drum 61 is provided in the upstream side of thesteam-condensate heat exchanger 21 that heats the rich solution 14. Inthe downstream side of the flash drum 61, the rich solution 14 washeated in the steam-condensate heat exchanger 21, to thereby increasethe temperature of the rich solution 14 to be supplied to theregeneration tower 15.

In example 3, as the result, the amount of steam consumed in theregeneration tower 15 became 97.27 MMkcal/h. Assuming the comparativeexample is 100, the amount of steam consumed in this example becomes98.5%. Therefore, the reduction rate of specific steam consumption(improvement effect) was 1.5%.

EXAMPLE 4

A CO2 recovery system according to example 4 of the present invention isexplained below with reference to the following drawing.

FIG. 13 is a schematic of the CO2 recovery system according to example4. Components the same as those of example 1 are assigned with the samereference numerals and explanation thereof is omitted.

In example 4, the rich solution 14 was divided, part of the richsolution 14 divided was sent to the heat exchanger 31 of flash drumtype, where the rich solution 14 was heat-exchanged with the steam fromthe steam condensate and CO2 was removed from the rich solution 14.Using the residual heat of the semi-lean solution 28 after the heatexchange, the other part of the rich solution 14 divided washeat-exchanged in the semi-lean-solution heat exchanger 29, to increasethe temperature of the rich solution 14 to be supplied to theregeneration tower 15.

In example 4, as the result, the amount of steam consumed in theregeneration tower 15 became 97.56 MMkcal/h. Assuming the comparativeexample is 100, the amount of steam consumed in this example becomes98.8%. Therefore, the reduction rate of specific steam consumption(improvement effect) was 1.2%.

EXAMPLE 5

A CO2 recovery system according to example 5 of the present invention isexplained below with reference to the following drawing.

FIG. 14 is a schematic of the CO2 recovery system according to example5. Components the same as those of example 1 are assigned with the samereference numerals and explanation thereof is omitted.

In example 5, the rich solution 14 was divided, and part of the richsolution 14 divided was sent to the heat exchanger 31 of flash drumtype, but on the way to the heat exchanger 31, the rich solution 14 washeat-exchanged with the residual heat of the steam condensate in thesteam-condensate heat exchanger 21, to improve the removal rate of CO2from the rich solution 14 in the flash drum 31. Using the residual heatof the semi-lean solution 28 after the heat exchange, the other part ofthe rich solution 14 divided was heat-exchanged in thesemi-lean-solution heat exchanger 29, to thereby increase thetemperature of the rich solution 14 to be supplied to the regenerationtower 15.

In example 5, as the result, the amount of steam consumed in theregeneration tower 15 became 95.52 MMkcal/h. Assuming the comparativeexample is 100, the amount of steam consumed in this example becomes96.7%. Therefore, the reduction rate of specific steam consumption(improvement effect) was 3.3%.

EXAMPLE 6

A CO2 recovery system according to example 6 of the present invention isexplained below with reference to the following drawing.

FIG. 15 is a schematic of the CO2 recovery system according to example6. Components the same as those of example 1 are assigned with the samereference numerals and explanation thereof is omitted.

In example 6, the regeneration tower 15 was divided into two portions,the semi-lean solution 28 extracted from the upper-portion regenerationtower 15-U was heat-exchanged with the residual heat of the steamcondensate 19 in the steam-condensate heat exchanger 21, and thesemi-lean solution 28 heat-exchanged was returned to the lower-portionregeneration tower 15-L. This caused an increase in the temperature ofthe semi-lean solution to be supplied to the lower portion side of theregeneration tower 15.

In example 6, as the result, the amount of steam consumed in theregeneration tower 15 became 93.65 MMkcal/h. Assuming the comparativeexample is 100, the amount of steam consumed in this example becomes94.8%. Therefore, the reduction rate of specific steam consumption(improvement effect) was 5.2%.

EXAMPLE 7

A CO2 recovery system according to example 7 of the present invention isexplained below with reference to the following drawing.

FIG. 16 is a schematic of the CO2 recovery system according to example7. Components the same as those of example 1 are assigned with the samereference numerals and explanation thereof is omitted.

In example 7, the regeneration tower 15 was divided into two portions,and the rich solution 14 was divided. The lean-solution heat exchanger23 was provided in the first rich-solution supply pipe 20-1, and in thedownstream side thereof, the steam-condensate heat exchanger 21 wasprovided, to thereby increase the temperature of the rich solution 14 tobe supplied to the lower-portion regeneration tower 15-L. Furthermore,the semi-lean-solution heat exchanger 29, which uses the residual heatof the semi-lean solution 28 fed from the upper-portion regenerationtower 15-U, was provided in the second rich-solution supply pipe 20-2,to thereby increase the temperature of the rich solution to be suppliedto the upper-portion regeneration tower 15-U.

The ratio of division of the rich solution 14 is such that the firstrich solution was set to 70% and the second rich solution was set to30%.

In example 7, as the result, the amount of steam consumed in theregeneration tower 15 became 93.58 MMkcal/h. Assuming the comparativeexample is 100, the amount of steam consumed in this example becomes94.8%. Therefore, the reduction rate of specific steam consumption(improvement effect) was 5.2%.

EXAMPLE 8

A CO2 recovery system according to example 8 of the present invention isexplained below with reference to the following drawing.

FIG. 17 is a schematic of the CO2 recovery system according to example8. Components the same as those of example 1 are assigned with the samereference numerals and explanation thereof is omitted.

In example 8, the regeneration tower 15 was divided into two portions,and the semi-lean solution 28 extracted from the upper-portionregeneration tower 15-U was first heat-exchanged in the firstlean-solution heat exchanger 23-1, and then, was heat-exchanged with theresidual heat of the steam condensate 19 in the steam-condensate heatexchanger 21, and the semi-lean solution 28 heat-exchanged was returnedto the lower-portion regeneration tower 15-L. This caused an increase inthe temperature of the semi-lean solution to be supplied to the lowerportion side of the regeneration tower 15.

In example 8, as the result, the amount of steam consumed in theregeneration tower 15 became 91.1 MMkcal/h. Assuming the comparativeexample is 100, the amount of steam consumed in this example becomes92.3%. Therefore, the reduction rate of specific steam consumption(improvement effect) was 7.7%.

EXAMPLE 9

A CO2 recovery system according to example 9 of the present invention isexplained below with reference to the following drawing.

FIG. 18 is a schematic of the CO2 recovery system according to example9. Components the same as those of example 1 are assigned with the samereference numerals and explanation thereof is omitted.

In example 9, the regeneration tower 15 was divided into four portionssuch as a first regeneration tower 15-1, a second regeneration tower15-2, a third regeneration tower 15-3, and a fourth regeneration tower15-4. The semi-lean solution 28 respectively extracted from the firstregeneration tower 15-1 and the third regeneration tower 15-3 washeat-exchanged with the respective residual heat of the steam condensatein a first steam-condensate heat exchanger 21-1 and a secondsteam-condensate heat exchanger 21-2, respectively. Because thetemperature in the lower portion side of the regeneration tower washigh, the residual heat of the steam condensate 19 was effectively used.

Furthermore, the semi-lean solution extracted from the secondregeneration tower 15-2 was heat-exchanged with the residual heat of thelean solution 16 in the first lean-solution heat exchanger 23-1. Thesemi-lean solution 28 extracted from the first regeneration tower 15-1,before being returned to the second regeneration tower 15-2 in the lowerstage side, was heat-exchanged in the second lean-solution heatexchanger 23-2 in which the semi-lean solution 28 was heat-exchangedwith the residual heat of the lean solution 16 that had beenheat-exchanged in the first lean-solution heat exchanger 23-1. Inexample 9, after the heat exchange, the rich solution 14 fed from theabsorption tower 13 was heat-exchanged in a third lean-solution heatexchanger 23-3.

In example 9, as the result, the amount of steam consumed in theregeneration tower 15 became 85.49 MMkcal/h. Assuming the comparativeexample is 100, the amount of steam consumed in this example becomes86.6%. Therefore, the reduction rate of specific steam consumption(improvement effect) was 13.4%.

EXAMPLE 10

A CO2 recovery system according to example 10 of the present inventionis explained below with reference to the following drawing.

FIG. 19 is a schematic of the CO2 recovery system according to example10. Components the same as those of example 1 are assigned with the samereference numerals and explanation thereof is omitted.

In example 10, the regeneration tower 15 was divided into three portionssuch as the upper-portion regeneration tower 15-U, the middle-portionregeneration tower 15-M, and the lower-portion regeneration tower 15-L.The semi-lean solution 28 extracted from the middle-portion regenerationtower 15-M was heat-exchanged with the residual heat of the steamcondensate in the steam-condensate heat exchanger 21. Part of thesemi-lean solution 28 extracted was supplied to the semi-lean-solutionheat exchanger 29 that heats the rich solution 14, where the residualheat of the semi-lean solution was effectively used.

Furthermore, the semi-lean solution 28 extracted from the upper-portionregeneration tower 15-U was heat-exchanged with the residual heat of thelean solution 16 in the first lean-solution heat exchanger 23-1.

The rich solution 14 heat-exchanged in the semi-lean-solution heatexchanger 29 was heat-exchanged in the second lean-solution heatexchanger 23-2 in which the rich solution 14 was heat-exchanged with theresidual heat of the lean solution 16 that had been heat-exchanged inthe first lean-solution heat exchanger 23-1.

In example 10, as the result, the amount of steam consumed in theregeneration tower 15 became 91.9 MMkcal/h. Assuming the comparativeexample is 100, the amount of steam consumed in this example becomes93.0%. Therefore, the reduction rate of specific steam consumption(improvement effect) was 7%.

EXAMPLE 11

A CO2 recovery system according to example 11 of the present inventionis explained below with reference to the following drawing.

FIG. 20 is a schematic of the CO2 recovery system according to example11. Components the same as those of example 1 are assigned with the samereference numerals and explanation thereof is omitted.

In example 11, the regeneration tower 15 was divided into two portionssuch as the upper-portion regeneration tower 15-U and the lower-portionregeneration tower 15-L. The semi-lean solution 28, extracted from theupper-portion regeneration tower 15-U, was used to heat the richsolution in the second rich-solution supply pipe 20-2, in thesemi-lean-solution heat exchanger 29. Thereafter, the semi-lean solution28 was divided, to be heat-exchanged with the residual heat of the steamcondensate in the steam-condensate heat exchanger 21 before beingsupplied to the lower-portion regeneration tower 15-L.

The rich solution in the first rich-solution supply pipe 20-1 washeat-exchanged in the first lean-solution heat exchanger 23-1, wasjointed with the other one to be heat-exchanged with the residual heatof the lean solution 16 in the second lean-solution heat exchanger 23-2,and was supplied to the regeneration tower 15.

In example 11, as the result, the amount of steam consumed in theregeneration tower 15 became 93.96 MMkcal/h. Assuming the comparativeexample is 100, the amount of steam consumed in this example becomes95.1%. Therefore, the reduction rate of specific steam consumption(improvement effect) was 4.9%.

EXAMPLE 12

A CO2 recovery system according to example 12 of the present inventionis explained below with reference to the following drawing.

FIG. 21 is a schematic of the CO2 recovery system according to example12. Components the same as those of example 1 are assigned with the samereference numerals and explanation thereof is omitted.

In example 12, the regeneration tower 15 was divided into three portionssuch as the upper-portion regeneration tower 15-U, the middle-portionregeneration tower 15-M, and the lower-portion regeneration tower 15-L.The semi-lean solution 28 extracted from the middle-portion regenerationtower 15-M was heat-exchanged with the residual heat of the steamcondensate in the steam-condensate heat exchanger 21.

Furthermore, the rich solution 14 was divided, and the lean-solutionheat exchanger 23 was provided in the first rich-solution supply pipe20-1. The semi-lean-solution heat exchanger 29 was provided in thesecond rich-solution supply pipe 20-2 where heat exchange was performedusing the semi-lean solution 28 extracted from the upper-portionregeneration tower 15-U, so that the residual heat of the semi-leansolution was effectively used.

In example 12, as the result, the amount of steam consumed in theregeneration tower 15 became 91.14 MMkcal/h. Assuming the comparativeexample is 100, the amount of steam consumed in this example becomes92.3%. Therefore, the reduction rate of specific steam consumption(improvement effect) was 7.7%.

Industrial Applicability

The CO2 recovery system according to the present invention is suitablefor reduction in the supply amount of heated steam used in theregeneration tower by effectively using the residual heat of the steamcondensate and the residual heat of the semi-lean solution.

The invention claimed is:
 1. A CO₂ recovery system including anabsorption tower that receives CO₂-containing gas and CO₂-absorbingsolution, and causes the CO₂-containing gas to come in contact with theCO₂-absorbing solution to produce CO₂ rich solution, and a regenerationtower, including an upper-portion regeneration tower and a lower-portionregeneration tower, that receives the rich solution and produces leansolution from the rich solution by removing CO₂ from the rich solution,the CO₂ recovery system comprising: a bottom lean-solution extractionpath that extracts lean solution that accumulates near a bottom portionof the regeneration tower from a first point of the regeneration towerand returns extracted lean solution to a second point of theregeneration tower that is downstream of the first point; a regenerationheater arranged in the bottom lean-solution extraction path and heatsthe lean solution in the bottom lean-solution extraction path withsaturated steam thereby producing steam condensate from the saturatedsteam; a steam-condensate heat exchanger that heats, with the steamcondensate, either one of (a) the rich solution that is supplied fromthe absorption tower to the regeneration tower, and (b) a semi-leansolution that is extracted outside from a middle portion of theregeneration tower and returned to the middle portion of theregeneration tower; a semi-lean-solution supply member that extractssemi-lean solution from a ninth point of the upper-portion regenerationtower and returns extracted semi-lean solution to a tenth point of theupper-portion regeneration tower that is downstream of the ninth point;a rich-solution supply member that conveys the rich solution from theabsorption tower to the regeneration tower; a first branching nodeprovided in the rich-solution supply member and that branches therich-solution supply member into a first rich-solution supply member anda second rich-solution supply member; a lean-solution supply member thatextracts the lean solution from the regeneration tower and conveysextracted lean solution to the absorption tower; a lean-solution heatexchanger that is provided in the first rich-solution supply member andthe lean-solution supply member, and heats the rich solution in thefirst rich-solution supply member with the lean solution in thelean-solution supply member; a semi-lean-solution heat exchanger that isprovided in the second rich-solution supply member and thesemi-lean-solution supply member, and heats the rich solution in thesecond rich-solution supply member with the semi-lean solution in thesemi-lean-solution supply member; a solution supply path that suppliesthe rich solution heated in the semi-lean-solution heat exchanger todownstream of the lean-solution heat exchanger in the firstrich-solution supply member; a second lean-solution heat exchangerarranged in the first rich-solution supply member and the lean-solutionsupply member downstream of where the solution supply path conveys therich solution in the first rich-solution supply member; and a secondbranching node provided in the semi-lean-solution extraction pathdownstream of the semi-lean-solution heat exchanger and that branchesthe semi-lean-solution extraction path into a first semi-lean-solutionextraction path and a second semi-lean-solution extraction path, whereinthe steam-condensate heat exchanger is arranged in the firstsemi-lean-solution extraction path and heats the semi-lean solution inthe first semi-lean-solution extraction path with the steam condensate,and one end of the second semi-lean-solution extraction path isconnected to a middle stage portion of the absorption tower.
 2. The CO₂recovery system according to claim 1, wherein the absorption tower isdivided into an upper stage and a lower stage, and the semi-leansolution to be supplied to a portion between the upper stage and thelower stage of the absorption tower is jointed with a semi-lean solutionextracted from the upper-stage absorption tower, to be supplied to thelower-stage absorption tower.